Plasma arc torches, also known as electric arc torches, are commonly used for cutting, marking, gouging, and welding metal workpieces by directing a high energy plasma stream consisting of ionized gas particles toward the workpiece. In a typical plasma arc torch, the gas to be ionized is supplied to a distal end of the torch and flows past an electrode before exiting through an orifice in the tip, or nozzle, of the plasma arc torch. The electrode has a relatively negative potential and operates as a cathode. Conversely, the torch tip constitutes a relatively positive potential and operates as an anode. Further, the electrode is in a spaced relationship with the tip, thereby creating a gap, at the distal end of the torch. In operation, a pilot arc is created in the gap between the electrode and the tip, which heats and subsequently ionizes the gas. Further, the ionized gas is blown out of the torch and appears as a plasma stream that extends distally off the tip. As the distal end of the torch is moved to a position close to the workpiece, the arc jumps or transfers from the torch tip to the workpiece because the impedance of the workpiece to ground is lower than the impedance of the torch tip to ground. Accordingly, the workpiece serves as the anode, and the plasma arc torch is operated in a “transferred arc” mode.
One of two methods is typically used for initiating the pilot arc between the electrode and the tip. In the first method, commonly referred to as a “high frequency” or “high voltage” start, a high potential is applied across the electrode and the tip sufficient to create an arc in the gap between the electrode and the tip. Accordingly, the first method is also referred to as a “non-contact” start, since the electrode and the tip do not make physical contact to generate the pilot arc. In the second method, commonly referred to as a “contact start,” the electrode and the tip are brought into contact and are gradually separated, thereby drawing an arc between the electrode and the tip. The contact start method thus allows an arc to be initiated at much lower potentials since the distance between the electrode and the tip is much smaller.
With contact start torches, however, the relative orientation and spacing of the electrode and the tip are critical to proper torch operation and cut quality, and providing a torch with a moving electrode and/or tip that retains the proper orientation and spacing during repeated operation is relatively difficult and expensive. Further, when a pilot arc is generated between the electrode and the tip proximate the bottom of the electrode, damage accumulates more rapidly on the tip near the orifice, which can negatively impact torch performance and cut quality. Additionally, with plasma arc torches in which the tip is movable, the tip is in different positions between the on and off modes, thereby causing difficulty in controlling the relative position of the tip with respect to the workpiece. Moreover, drag cutting, which requires the tip to be in contact with the workpiece, becomes difficult if not impossible since the tip would be moved back into contact with the electrode upon being placed into contact with the workpiece.
One known contact start plasma arc torch design employs a stationary electrode and tip, while a translatable swirl ring is in initial contact with the electrode and moves away to draw an arc between the electrode and the tip. However, such a starting method causes damage to accumulate more rapidly on the swirl ring, or the anodic element, thereby reducing the life of the swirl ring and resulting in reduced torch performance. Further, with a swirl ring as a translatable element, the gas dynamics inside the torch may be negatively impacted if the translatable swirl ring becomes misaligned and also as the translatable swirl ring becomes worn during operation. Moreover, repair or replacement of the translatable swirl ring is relatively difficult as several components within the distal end of the torch must be removed for access.
Accordingly, a need remains in the art for a contact start plasma arc torch and associated methods that reduce the amount of damage to the electrode and the tip while increasing torch performance. A further need exists for such a torch that provides for quick and efficient replacement of consumable components, (e.g., electrode, tip), disposed therein.